More than a dozen scientists Wednesday called for a global moratorium on experiments and studies into creating designer babies — but one key signature was missing.

Eighteen ethicists and scientists from seven countries urged the international community to halt “all clinical uses of human germline editing — that is, changing heritable DNA (in sperm, eggs or embryos) to make genetically modified children,” the statement read in science journal Nature.

Signatories included Eric S. Lander, a geneticist and the founder of the Broad Institute of MIT and Harvard; Feng Zhang, the co-creator of CRISPR-Cas9; and Canadian bioethicist Francoise Baylis.

Missing from the group of 18, however, was Jennifer Doudna.

Doudna was one of the scientists who created CRISPR-Cas9, a gene-editing technology that allows researchers to permanently modify genes in living cells and organisms.

In March 2015, she spoke out against the unethical uses of her technology, cautioning that more discussion amongst scientists, clinicians, the public and government must happen. On top of that, she and others in the scientific community warned that splicing and editing sperm and egg cell DNA could have unintended consequences because the technology and science is so new.

However, those warnings seemed to have fallen on deaf ears when, in November 2018, news came out of China that a researcher edited the DNA of human embryos and as a result, a set of twin girls were born. The twins were the first ever known, genetically modified babies born into the world. The researcher, He Jiankui, said he edited the DNA so that the babies would be resistant to HIV.

The experiment was denounced by many in the scientific community around the world, some calling it crazy and deeming He a “rogue” actor.

At the time, Doudna told Bloomberg she was “horrified” and disappointed in the way He used the technology, saying it was inappropriate and not medically necessary.

In response to the letter put out in Nature, Doudna said she felt signing on would just be “rehashing” what’s already been said, The Washington Post reported. Instead, she took a different stance and said she will continue working with national academies in the United States, U.K. and China.

“I prefer this to a ‘moratorium’ which, to me, is of indefinite length and provides no pathway toward possible responsible use,” Doudna said in an email to the National Post. “Open discussion and transparency around this important topic should be encouraged, not suppressed.”

The letter advises that there should be a fixed period where no germline editing should be allowed. Until that period is over, “discussions about the technical, scientific, medical, societal, ethical and moral issues… must be considered before germline editing is permitted,” the paper reads.

It also calls on international cooperation to oversee the use of gene editing technology. It doesn’t call for a ban on research into germline editing, but says the cells should not be used to impregnate someone.

The authors noted that unintended consequences of gene editing is “unacceptably high” and it must be fully understood before doing any experiments that enhance humans. They pointed to the gene SLC39A8, which decreases a person’s risk of Parkinson’s disease and hypertension but increases their risk of developing schizophrenia, Crohn’s disease and obesity.

With that, the authors said enhancing humans to, for example, see in infrared is highly warned against because the unintended consequences aren’t known.

“Individuals with genetic differences or disabilities can experience stigmatization and discrimination. Parents could be put under powerful peer and marketing pressure to enhance their children. Children with edited DNA could be affected psychologically in detrimental ways. Many religious groups and others are likely to find the idea of redesigning the fundamental biology of humans morally troubling. Unequal access to the technology could increase inequality. Genetic enhancement could even divide humans into subspecies.”

The authors call on nations to voluntarily pledge that they will not allow germline editing until certain requirement are met. They reason that previous frameworks haven’t or would not work. International treaties to ban clinical use of genetic editing except in some extenuating circumstances would be difficult to agree to and enforce, the letter states.

Instead, voluntarily pledging and creating a coordinating body that hosts a range of stakeholders including scientists, ethicists, the public and governments would allow for countries to take on germline editing according to their own needs, cultures, values and so on, the authors argue.